Semiconductor device

ABSTRACT

A semiconductor device having a current blocking layer and confinement current passing part formed on a semiconductor layer, and an electrode metal layer disposed on said current blocking layer and confinement current passing part, wherein the current blocking layer is made of semiconductor material, and the contact resistance of current blocking layer and electrode metal layer is higher than the contact resistance of electrode metal layer and semiconductor layer, and/or the resistivity of the current blocking layer is higher than that of the semiconductor layer.

BACKGROUND OF THE INVENTION

This invention relates to an improved structure of the electrode portionin a semiconductor possessing a current blocking layer.

As current confinement means in a semiconductor device, it is known toform a confinement current passing part in a size suited to the currentpassage in an insulation film of SiO₂, SiN_(x) or the like, and toevaporate an electrode metal layer thereon.

As its practical example, one as shown in FIG. 7 has been alreadypresented.

In the semiconductor laser device in FIG. 7, an n-type layer 2, InGaAsPactive layer 3, p-type layer 4, and InGaAsP contact layer 5 aresequentially grown on the upper surface of an n-type InP substrate 1,and an SiO₂ insulation film 6 is evaporated on the InGaAsP contact layer5, and a part of the SiO₂ insulation film 6 is removed in a window formby etching means so as to expose the surface of the InGaAsP contactlayer 5, thereby forming a confinement current passing part 9, and thena p-type electrode metal layer 7 is evaporated on the surface of InGaAsPcontact layer 5 and on the SiO₂ insulation film 6, and an n-typeelectrode metal layer 8 is evaporated on the lower surface of the n-typeInP substrate 1.

In the case of thus fabricated semiconductor laser device, by applying avoltage between the p-type electrode metal layer 7 and the n-typeelectrode metal layer 8, the current passes only through the confinementcurrent passing part 9 disposed on the SiO₂ insulation film 6 and flowsto the side of n-type electrode metal layer 8, and this current emitslight when passing through the InGaAsP active layer 3.

This light emitting portion is nearly equal to or larger than theconfinement current passing part 9.

In such prior art, however, the following technical problems are leftunsolved.

That is, the coefficient of thermal expansion of insulation film 6 ofSiO₂, SiN_(x) or the like is smaller by one or two digits than thecoefficient of thermal expansion of a compound semiconductor, and alongwith the temperature rise when injecting current, the stress isconcentrated on the end portion of the dielectric film 6, and a defectoccurs in the contact layer 5.

This defect propagates up to the active layer 3 along the crystaldirection of the semiconductor crystal, and deteriorates the lightemission efficiency of the semiconductor laser device.

SUMMARY OF THE INVENTION

In the light of such technical problem, it is hence a primary object ofthis invention to present a highly reliable semiconductor deviceexcelling in quality and characteristics, and also capable of achievinga sufficient current confinement by inhibiting the leakage current inthe portion other than the confinement current passing part.

The semiconductor device according to the present invention has, inorder to achieve the above object, a current blocking layer andconfinement current passing part formed on a semiconductor layer, andelectrode metal layer disposed on said current blocking layer andconfinement current passing part, wherein the current blocking layer ismade of semiconductor material, and the contact resistance of currentblocking layer and electrode metal layer is higher than the contactresistance of electrode metal layer and semiconductor layer, and/or theresistivity of current blocking layer is higher than that of thesemiconductor layer.

According to a preferred embodiment, the semiconductor device has aninsulation film possessing a current confinement window wider in windowarea than the current confinement window of the current blocking layer,intervening between the current blocking layer and electrode metallayer.

In the semiconductor device, the resistance value r_(b) of the currentblocking layer or semiconductor itself is expressed in equation (1)below, supposing its own resistivity to be ρ, area to be S and thicknessto be l, and the contact resistance r_(c) generated between the current

i blocking layer and the semiconductor or electrode metal layer isexpressed in equation (2), supposing the resistance value per unit areabetween the two to be R and contact area to be S.

    r.sub.b =ρ·l/S                                (1)

    r.sub.c =R/S                                               (2)

Therefore, the total resistance value r between the electrode metallayer and current blocking layer, or the confinement current passingpart and its lower semiconductor layer is expressed as r_(b) +r_(c).

Meanwhile, the contact resistance between the current blocking layer orconfinement current passing part and its lower semiconductor layerappears to be a problem, but it is the mutual contact resistance ofsemiconductors and therefore can be ignored.

In the case of the semiconductor device according to the specificinvention, a confinement current is injected from the electrode metallayer to the semiconductor layer, for example, from the electrode metallayer to the confinement current passing part of the current blockinglayer and to the semiconductor layer.

In this case, the current blocking layer (semiconductor material) ismade of such a semiconductor material that its contact resistance valuer₁ with the electrode metal layer (metal conductor) is higher than thecontact resistance value r₂ of the electrode metal layer andsemiconductor layer, and/or that the resistivity p₁ of the currentblocking layer is higher than the resistivity p₂ of the semiconductorlayer, and moreover the coefficient of thermal expansion of the currentblocking layer is same as the coefficient of thermal expansion of thesemiconductor layer, therefore, if a temperature rise should occur inthe semiconductor device when injecting the current, internal stress anddefect hardly occur, and deterioration of characteristics of thesemiconductor device is scarcely noted.

Incidentally, in the semiconductor device of the specific invention, ifthe contact resistance value r₁ (or resistivity p₁) is not sufficientlyhigher than the contact resistance value r₂ (or resistivity p₂) and thearea S1 of the current confinement part is wider than the area S2 of theconfinement current passing part, it is difficult to inhibit the leakagecurrent in other portion than the confinement current passing part, andit is hard to achieve a sufficient current confinement.

For example, in the case of a semiconductor device measuring 500 μm by500 μm, with the inside diameter of the current confinement part of 25μm, the radio S1/S2 reaches as far as 10³ approximately, and to achiever1/R2 of approximately 10³ by raising the purity of the current blockinglayer, the technical difficulty is extremely high.

In the semiconductor device by the related invention, since the majorityof the current blocking layer is covered by the insulation film of SiO₂,SiN_(x) or the like in the semiconductor device of the specificinvention, Si can be substantially decreased.

In other words, in the case of the related invention, an insulation filmpossessing a current confinement window (the first confinement window ofS1+S2) wider in the window area than the current confinement window (thesecond current confinement window with an area of S2) of the currentblocking layer is intervening between the current blocking layer and theelectrode metal layer, and moreover the confinement current passing partdetermined by the second current confinement window settles within theconfinement current passing part determined by the first currentconfinement window.

Explaining this in the aforementioned relation, the area of thesubstantial current blocking part S1 and the area of the confinementcurrent passing part is S2, and for example it is possible to set therelation of S1/S2<10, or when set as r₁ /r₂ =10, the leakage current canbe reduced.

A known example of r₁ /r₂ =10 is described in details in The Bell SystemTechnical Journal, Volume 62, Number 1, pages 1 to 25 (January 1983),"InGaAsP LEDs for 1.3-μm Optical Transmission."

In this publication, it is mentioned, for example, that R_(InP)/R_(InGaAs) can be set at 7 to 8 as the current blocking layer.

Furthermore, in the semiconductor device of the related invention, if astress is caused inside the first current confinement window of theinsulation film due to current injection, the stress concentratedportion at this time is sufficiently outside of the confinement currentpassing part by the second current confinement window, any defect is notformed in the confinement current passing part, and nonlight emittingphenomenon derived from the defect may be avoided, and the reliabilityof the semiconductor device may be further enhanced.

Some of the embodiments of semiconductor device according to thisinvention will now be described in details with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a first embodiment of the semiconductordevice of the invention.

FIG. 2 (A), (B), (C) are principal process drawings for fabricating thesemiconductor device in FIG. 1.

FIG. 3 is a sectional view showing a second embodiment of thesemiconductor device of the invention.

FIGS. 4 and 5 are a plan view and a sectional view showing a thirdembodiment of the semiconductor device of the invention.

FIG. 6 is a sectional view of essential parts showing a fourthembodiment of the semiconductor device of the invention.

FIG. 7 is a sectional view showing a conventional semiconductor device.

FIG. 8 is a explanatory drawing showing the result of current passingtest of the semiconductor device (LED) of the invention.

FIG. 9 is a explanatory drawing of dark line formed in a conventionalsemiconductor device (LED).

First, the semiconductor device shown in FIG. 1 is explained.

In FIG. 1, numeral 11 denotes an n-type InP substrate having an InPbuffer layer, 13 is an InGaAsP active layer formed on this n-type InPsubstrate 11, and 13 is an InP (or ZnInP)-clad layer formed on thisInGaAsP active layer 12.

On the InP clad layer 13, in its middle part, a mesa-shaped InGaAsPcontact layer 14 is formed, and around this mesa-shaped InGaAsP contactlayer 14, an n-type InP (or Fe -doped InP, nondoped InP) buried layer 15is formed, and on this n-type InP buried layer 15, an insulation film 16made of silicon dielectric such as SiN₂, SiO₂ and amorphous Si isformed.

In this constitution, the opening in the middle of the siliconinsulation film 16 is enclosed by the first current confinement window17 and the buried layer 15, where a second current confinement window 18is formed, and in the relative relation of the first current confinementwindow 17 and second current confinement window 18, the window area ofthe first current confinement window 17 is wider than the window area ofthe second current confinement window 18.

Moreover, in order to cover the upper surfaces of the silicon insulationfilm 16, n-type InP buried layer 15, and InGaAsP contact layer 14,p-type electrode metal layers 19 of Ti, Pt, Au or their alloy areprovided on these surfaces, while an n-type electrode metal layer 20made of the above metal conductor is disposed on the lower surface ofthe n-type InP substrate 11.

Referring then to FIG. 2 (A), (B), (C), an example of fabrication of thesemiconductor device shown in FIG. 1 is explained below.

First, as shown in FIG. 2 (A), on the n-type InP substrate, an InPbuffer layer (not shown), InGaAsp active layer 12, InP or ZnInP cladlayer 13, InGaAsP contact layer 14, and SiO₂ etching mask 10 aresequentially formed.

In this case, the crystal layers are formed by epitaxial growth ofspecified crystal by crystal growth means such as LPE, VPE, MOCVD andMBE, while the SiO₂ etching mask 10 is formed through, for example,sputtering means.

Next, as shown in FIG. 2 (B), by patterning by the technique ofphotolithography, the undesired parts of the InGaAsP contact layer 14and SiO₂ etching mask 10 are removed.

Afterwards, as shown in FIG. 2 (C), an n-type buried layer 15 such asInP or Fe-doped InP, nondoped InP is formed in the etching portionsformed at both sides of the mesa-shaped InGaAsP contact layer 14 throughthe crystal growth means mentioned above.

In this case, since the upper surface of the InGaAsP contact layer 14 iscovered with SiO₂ etching mask 10, the layer of InP is not formed on theupper surface, and therefore the InGaAsP contact layer 14 is buried intothe n-type InP buried layer 15.

Thereafter, from the upper surface of the InGaAsP contact layer 14 fromwhich the SiO₂ etching mask 10 is removed to the upper surface of then-type InP buried layer 15, a silicon insulation film 16 such asSiN_(x), SiO₂ and amorphous Si is formed by sputtering, and afteropening a window in the middle part of the silicon insulation film 16,p-type electrode metal layers 19 of Ti, Pt, Au or the like areevaporated on the upper surfaces of the InGaAsP contact layer 14, n-typeInP-buried layer 15 and silicon insulation film 16, and similarly ann-type electrode metal layer 20 of the same metal conductor isevaporated on the lower surface of the n-type InP substrate 11.

In this way, the semiconductor device as shown in FIG. 1 is obtained Insuch laminate structure of the semiconductor device, any large stepdifference of over 1 μm is not formed between the middle and peripheryof the p-type electrode metal layer 19, and breakage of the p-typeelectrode metal layer 19 due to step difference does not occur, andstill more only by inverting the conductive type of the InP-buried layer15 from that of the InP clad layer 13, a current confinement effect byP-N junction can be achieved in this buried layer 15.

In the semiconductor device in FIG. 1, when a voltage is applied betweenthe p-type electrode metal layer 19 and the n-type electrode metal layer20, the injection current is constricted within the range of secondcurrent confinement window 18, and the specified portion of the InGaAaPactive layer 12 corresponding to it emits light.

In such semiconductor device, should defects X occur in thesemiconductor layer near the inner circumference of the first currentconfinement window 17 in the silicon insulation film 16, such defects Xare located outside the substantial confinement current passing part bythe second current confinement window 18, and hence nonlight emittingpart is not formed within this light emitting region.

Next is described the semiconductor device shown in Fig. 3.

In FIG. 3, numeral 21 denotes an n-type InP substrate, 22 is an n-typeInP-clad layer, 23 is an InGaAsP active layer, 24 is a p-type InP-cladlayer, 25 is a p-type InGaAsP contact layer, 26 is a high resistanceInP-blocking layer, and 27 is an SiO₂ dielectric film, and these layersand films are formed in the specific sequence and at specific positionson the n-type InP substrate 21.

In this constitution, a first current confinement window 28 is formed onthe SiO₂ dielectric film 27, and a second current confinement window 29is formed on the InP blocking layer 26.

In the relative position of the first current confinement window 28 andthe second current confinement window 29, the window area of the firstcurrent confinement window 28 is wider than the window area of thesecond current confinement window 29.

Furthermore, on the upper surface of the semiconductor layer grown onthe n-type InP substrate 21, a p-type electrode metal 30 made of Ti, Pt,Au or their alloy is disposed, while on the lower surface of the n-typeInP substrate, an n-type electrode metal layer 31 of the same metalconductor is disposed.

An example of fabricating the semiconductor device shown in FIG. 3 isexplained below.

First, through the crystal growth means, n-type InP clad layer 22,InGaAsP active layer 23, p-type InP-clad layer 24, p-type InGaAsPcontact layer 25, and InP-blocking layer 26 are sequentially formed onan n-type InP substrate 21 by epitaxial growth, and an SiO₂ insulationfilm 27 is formed on the InP blocking layer 26 by sputtering.

Next, through the etching means using a fluoric etchant, a first currentconfinement window 28 with window diameter of 30 μm is opened in theSiO₂ insulation film 27, and a second current confinement window 29 withwindow diameter of 30 μm in the InP-blocking layer 26, and the SiO₂insulation film 27 is further etched to widen the window diameter of thefirst current confinement window 28 to 40 μm.

Afterwards, on the upper surface of the semiconductor layer grown on then-type InP substrate 21, a p-type electrode metal layer 30 isevaporated, while an n-type electrode metal layer 31 is evaporated onthe lower surface of the n-type InP substrate 21, thereby obtaining thesemiconductor device in FIG. 3.

In the semiconductor device in FIG. 3, when a voltage is applied betweenthe p-type electrode metal layer 30 and the n-type electrode metal layer31, same as in the above embodiment, the infection current is contractedwithin the range of the second current confinement window 29, and aspecified portion of the InGaAsP active layer 23 corresponding to itemits light.

In such semiconductor device, should defects X occur inside of the firstcurrent confinement window 28 in the SiO₂ insulation film 27, suchdefects X are located outside the substantial confinement currentpassing part by the second current confinement window 29 and are alsoremote from the light emitting portion by as far as about 5 μm, andhence non-light emitting portion will not be formed within the lightemitting region.

Incidentally, in the semiconductor device in FIG. 3 according to thisembodiment, when an electric current of 150 mA was passed for 5000 hoursat 160° C. as shown in FIG. 8, the change in power was not more than 5%,and formation of dark line (non-light emitting portion) was notrecognized.

By contrast, in the conventional semiconductor device (FIG. 7), when anelectric current of 100 mA was passed for 20 hours at 160° C., the powerdeterioration was over 10%, and multiple dark lines corresponding to thecrystal position 100 were formed in the light emitting part as shown inFIG. 9.

Another semiconductor device is shown in FIGS. 4, 5.

In FIGS. 4, 5, numeral 41 is an n-type InP substrate, 42 is an InGaAsPactive layer, 43 is an InP clad layer, 44 is a p-type InGaAsP gap layer,43 is an InP clad, 44 is a p-type InGaAsP cap layer, 45 is anInP-blocking layer, and 46 is an SiO₂ insulation film, and these layersand films are formed on the n-type InP substrate in a specific sequenceand at specified positions.

The InGaASP active layer contains a cross type optical waveguide 51possessing four branching ends 47, 48, 49, 50, and a p-type Zn diffusionregion 52 is provided in the p-type InGaAsP gap layer 44 andInP-blocking layer 45.

A first current confinement window 53 is formed in the SiO₂ insulationfilm 46, and a second current confinement window 54 in the InP-blockinglayer 45.

In the relative relation of the first confinement window 53 and thesecond current confinement window 54, the window area of the firstcurrent confinement window 53 is wider than the window area of thesecond current confinement window 54.

Furthermore, on the upper surface of the semiconductor layer grown onthe n-type InP substrate 41, a p-type electrode metal layer 55 and anelectrode 56 for control current made of Ti, Pt, Au or their alloy aredisposed, while an n-type electrode metal layer 57 of the same metalconductor is provided or the lower surface of the n-type InP substrate41.

The semiconductor device shown in FIGS. 4, 5 is a current injection typephoto switch.

In the case of such semiconductor device, an electric current of 10kA/cm² is injected in stripes in the cross part of the optical waveguide51 so as to provide this cross part with light reflectivity (cross partcarrier high density=refractive index drop), or when current injectionis reduced or stopped to recover the light transmissivity of the crosspart possesses light reflectivity, the guide light entering the opticalwaveguide 51 from the branch end 47 is reflected in the cross part to beemitted from the branch end 48, and, to the contrary, when the crosspart possesses light transmissivity, the guide light entering theoptical waveguide 51 from the branch end 47 is allowed to move(penetrating through the cross part) to be emitted from the branch end48.

The semiconductor device shown in FIGS. 4, 5 can be used as currentinjection type widely in the whole field of OEIC in combination withFET, LED, LD, etc.

The semiconductor shown in FIGS. 6 is described below.

In FIGS. 6, numeral 61 denotes an InP semiinsulated substrate doped withFe, 62 is an n-type InGaAsP channel layer formed on this InPsemiinsulated substrate 61, 63 is a nondoped InP-blocking layer formedon the n-type InGaAsP channel layer 62, and 64 is an SiO₂ insulationfilm formed on the InP-B3 layer 63, and these layer and films are formedon the InP semiinsulated substrate 61 in a specific sequence and atspecific positions.

In this constitution, a p-type Zn diffusion region 65 is provided in then-type InGaAsP channel layer 62, and a first current confinement window66 is formed in the SiO₂ insulation film 64 and a second currentconfinement window 67 in the InP-blocking layer 63.

In the relative relation of the first current confinement window 66 andsecond current confinement window 67, too, the window area of the firstcurrent confinement window 66 wider than the window area of the secondcurrent confinement window 67.

On the upper surface of the semiconductor layer laminated on the InPsemiinsulated substrate 61, an electrode metal layer 68 made of Ti, Pt,Au or their alloy is disposed.

The semiconductor device shown in FIG. 6 is an FET, and when a biasvoltage is applied to a specific portion of such semiconductor devicewith the terminals of source, gate and drain being connected, thecarrier flows through the n-type InGaAsP channel layer 62 in a specifieddirection, and the current flows from the source side to the drain side,and in this embodiment in FIG. 6, the first current confinement window66 and second current confinement window 67 are similarly disposed, sothat the reliability of the source electrode and drain electrode when alarge current flows in and out can be enhanced.

In the semiconductor device of the specific invention, as stated herein,the current blocking layer is made of semiconductor material, and theelectric characteristic (resistance) of this current blocking layer isproperly determined in the relative relation with the electrode metallayer, so that the reliability of quality and characteristics may beenhanced, while the product yield may be also improved. Furthermore, inthe semiconductor device of the related invention, since a silicondielectric film possessing a current confinement window wider in windowarea than the current confinement window of the current blocking layeris intervening between the current blocking layer and electrode metallayer in the above specific invention, deterioration of characteristicsdue to the defects introduced into the semiconductor layer may beavoided more securely.

It is to be understood that the above-mentioned embodiments are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alterations may be made by thoseskilled in the art without departing from the spirit and scope of theinvention, and the appended claims are intended to cover suchmodifications and alterations.

What is claimed is:
 1. A semiconductor device comprising:an active layerformed on a semiconductor substrate; an electrode; a first semiconductorlayer in contact with the electrode; a first current blocking layerformed on the first semiconductor layer and having a current confinementwindow; wherein the contact resistance between the current blockinglayer and the electrode is higher than the contact resistance betweenthe electrode and the first semiconductor layer; and a second currentblocking layer formed on said first blocking layer and provided with adielectric insulation material having a window portion with an arealarger than that of the current confinement window.
 2. A semiconductordevice according to claim 1, wherein the first semiconductor layer is acontact layer.
 3. A semiconductor device according to claim 1, whereinthe first semiconductor layer is a cap layer.
 4. A semiconductor deviceaccording to claim 1, wherein said window portion is contiguous to saidfirst current blocking layer and an electrode is provided in the windowportion.
 5. A semiconductor device comprising:a semiconductor substrate;an active layer formed on the semiconductor substrate; an electrode afirst current blocking layer formed on said first semiconductor layerand having a current confinement window; the resistance of the currentblocking layer being higher than the contact resistance between theelectrode and the first semiconductor layer; and a second currentblocking layer formed on the first blocking layer and provided with adielectric insulating material having a window portion with an arealarger than that of said window.
 6. A semiconductor device according toclaim 5, wherein the first semiconductor layer is a contact layer.
 7. Asemiconductor device according to claim 5, wherein the firstsemiconductor layer is a cap layer.
 8. A semiconductor devicecomprising:an active layer formed on a semiconductor substrate; a firstsemiconductor layer contacting with an electrode; a first currentblocking layer formed on a cavity of said first semiconductor layerformed by removing a portion with only a current confinement windowunremoved; wherein the contact resistance between the first currentblocking layer and the electrode is higher than that between saidelectrode and the first semiconductor layer a second current blockinglayer including the unremoved portion of said first current blockinglayer and provided with a dielectric insulation material having a windowportion with an area larger than said unremoved portion; said first andsecond current blocking layers and said electrode being formed in theorder listed.
 9. A semiconductor device according to claim 8, whereinthe first semiconductor layer is a contact layer.
 10. A semiconductordevice according to claim 8, wherein the first semiconductor layer is acap layer.
 11. A semiconductor device according to claim 8, wherein thefirst current blocking layer being formed by a semiconductor materialwith higher contact resistance than that between said firstsemiconductor layer and said electrode.
 12. A semiconductor deviceaccording to claim 11, wherein the first semiconductor layer is acontact layer.
 13. A semiconductor device according to claim 11, whereinthe first semiconductor layer is a cap layer.